3V Boost Converter with MCP1640
Efficient boost switching regulator for battery operation
While searching for an efficient boost switching regulator for a battery-powered application, I came across Microchip's MCP1640. This can generate an output voltage of 3.3V over a wide input voltage range from a single 1.5V alkaline cell. The starting voltage is as low as 0.65V. If only small currents are required, or if the input voltage is higher (e.g. 2 cells alkaline or 1 cell lithium), an output voltage of 5V can also be achieved. To be able to test the chip as easy as possible, the module described in the following was built.
The circuit is minimalistic. The two capacitors C1 and C2 filter the pulses of the switching regulator. The voltage is stepped up with the storage choke L1 of IC1. The MCP1640 already integrates the field effect transistor necessary for a boost converter, as well as the matching rectifier diode. The voltage divider consisting of R2 and R3 determines the output voltage. It should be relatively high impedance to keep the quiescent current low. The given values are calculated for 3.3 volts. With the enable pin IC1 can be switched off completely. If this function is not used, the pin must be connected to the battery voltage. This can be realized by equipping R1 with 0 Ohm. All voltages as well as the enable pin are led out on a four pin header. Thus, the design can be used on the breadboard without any problems.
The circuit board was manufactured at Aisler. It is plated through on both sides and measures 12x20mm. The SMD components in design 1206 (capacitors) and 0603 (resistors) can be assembled by hand with a little practice. The coil has contacts on the bottom side, and must therefore be soldered with solder paste (alternatively tinned by hand) and hot air.
The measured quiescent current consumption at a fresh 1.5V AA battery is about 65µA. The 19µA specified in the datasheet are not achieved in my setup. Maybe the current consumption can be optimized by selecting different components.